For individuals aiming to excel in the field of software development, understanding Core Java is fundamental. Whether you’re getting ready for an interview or just want to get better at programming in Java, a structured Java course can help you a lot.
Java is the most widely used programming language in the current IT industry. A big reason why so many people are interested in and already working in programming is that knowing Java can help them get jobs. This article is dedicated to the same purpose. There is a full guide here to help you answer the most common Core Java interview questions.
Java is one of the most popular and widely used programming languages in the world. Its platform independence, object-oriented features, robustness, and high performance make it a top choice for enterprise applications. As a result, Java skills are highly sought after by tech companies and startups.
If you have an upcoming Java interview, you need to be well prepared to convince the interviewers that you have in-depth Java knowledge and skills. In this comprehensive guide, we will provide tips, sample questions, and answers to help you ace Java interview questions.
Why Learn Java for Interviews?
Here are some key reasons why Java is a must-have skill for interviews
-
Java is used by over 3 billion devices worldwide Knowing Java increases your chances of getting hired
-
Most top tech companies like Google, Amazon, Netflix, Uber, Twitter use Java extensively in their tech stacks.
-
Java is the #1 choice for developing Android apps, which dominate the mobile OS market.
-
Investment banks, trading firms, and startups use Java to build complex, distributed systems.
-
Java developers are among the highest paid software engineering profiles. Learning Java can significantly boost your career growth.
In short, having strong Java knowledge makes you a very sought after programmer and helps land your dream job.
Frequently Asked Java Interview Questions
Let’s look at some of the most commonly asked Java interview questions for freshers as well as experienced developers:
Java Basics
Q1. What is Java? What are its main features?
Q2. What is JVM and how does it work?
Q3. What is bytecode in Java?
Q4. What are the important Java concepts like object, class, abstraction, inheritance, etc?
Q5. What are wrappers in Java? Why are they used?
Q6. What is method overloading and overriding in Java?
Q7. What is final keyword in Java?
OOPs Concepts
Q8. Explain Inheritance, Encapsulation, Abstraction, and Polymorphism in Java.
Q9. Difference between abstract classes and interfaces in Java.
Q10. What is Object class in Java and why is it important?
Q11. Can we have a class inside a method in Java?
Q12. What is object cloning in Java?
Java Collections Framework
Q13. What are the important interfaces and classes in Java Collections like List, Set, Map, etc?
Q14. Difference between Array and ArrayList in Java.
Q15. Difference between HashMap and Hashtable in Java.
Q16. How HashMap works internally in Java?
Q17. What is difference between Array and LinkedList?
Multithreading and Concurrency
Q18. What is multithreading in Java?
Q19. Lifecycle and states of a thread in Java.
Q20. What is race condition and how can we avoid it?
Q21. What are wait, notify and notifyAll in Java?
Q22. What are volatile and atomic variables in Java?
Exceptions and Error Handling
Q23. Different types of exceptions in Java.
Q24. Checked vs unchecked exceptions.
Q25. Important methods of Throwable class.
Q26. finally block in Java.
Q27. try-with-resources in Java.
Java 8 Features
Q28. What are the major features introduced in Java 8?
Q29. What are lambda expressions in Java 8?
Q30. How does Java 8 handle functional programming?
Q31. Method references in Java 8.
Q32. forEach loop in Java 8.
Java Design Patterns
Q33. What are Singleton, Factory, and Builder design patterns?
Q34. When to use Strategy, Observer, and Decorator patterns?
Q35. Main uses cases of Proxy, Composite and Flyweight patterns.
Java IO and NIO
Q36. Difference between IO streams and NIO in Java.
Q37. Reading and writing files using Byte Streams.
Q38. What are the important classes in Java NIO?
Java Database Connectivity
Q39. What is JDBC API? What are its important interfaces and classes?
Q40. Steps to connect to a database in Java.
Q41. Difference between Statement and PreparedStatement.
Q42. What is ORM and how can you use it with Java?
Java Memory Management
Q43. What is Java Garbage Collection? How does it work?
Q44. What are different types of GC algorithms like Serial vs Parallel GC?
Q45. What are the main memory areas in JVM?
Q46. What is PermGen space in Java?
Java Best Practices
Q47. What are immutable classes in Java and where are they useful?
Q48. How to avoid NullPointerExceptions in Java?
Q49. Using logging frameworks like Log4j and SLF4J.
Q50. Best practices for exception handling in Java.
Tips to Crack Java Interview Questions
Here are some useful tips to help you prepare for Java interview questions:
-
Revise core Java concepts like OOPs, Collections, Multithreading, NIO etc thoroughly. These form the basics of Java programming.
-
Practice important algorithms and data structures like arrays, linked lists, trees, graphs, sorting, searching, etc. These are frequently asked in interviews.
-
Work on Java programming problems on LeetCode, GeeksforGeeks, Hackerrank, etc to improve logic and speed.
-
Go through Java design patterns as they demonstrate object oriented analysis and design skills.
-
Work on Java projects to get hands-on coding experience in building real world apps.
-
Be thorough with your resume projects. Interviewers often ask deeper questions on them.
-
Review Java interview questions on web. Identify your weak areas and prepare those topics.
-
Do mock interviews with friends or mentors to gain confidence and feedback.
-
Stay calm and confident during interviews. Clarify doubts politely if you don’t understand any question.
If you follow these tips and prepare diligently, you can master Java fundamentals as well as programming skills. This will help you succeed in landing your dream Java developer job.
So what are you waiting for? Start prepping today and get ready to ace those Java interviews! Best of luck!
18 Does Java work as a “pass by value” or “pass by reference” phenomenon?
Java works as a “pass-by-value” phenomenon. This means that when we give an object to a method, we’re really giving it a copy of its reference.
For example, lets consider the following code:
public void changeValue(int x) {
   x = 5;
int num = 10;
In this code, we pass the value of num to the changeValue() method. If we change the value of x inside the method, however, it doesn’t change the value of num outside the method. This is because Java passes a copy of the value of num, not the actual object. Â.
4 How is the ânew’ operator different from the ânewInstance()’ operator in java?
Both the new operator and the newInstance() method are used to create objects in Java. If we know what kind of object we want to make, we can use the new operator. If we don’t know what kind of object we want to make until runtime, we need to use the newInstance() function.
